1. Field of the Invention
The invention relates to the fabrication of a durable, but water soluble; non-toxic coating which may be applied to and removed from radio-lucent medical stents. In particular, this coating allows the radiographic imaging of the stents mounted on teeth in a patient's mouth, and such stents may be used to position and to guide the placement of dental implants.
2. Description of the Related Art
The placement of an implant-retained dental restoration in a patient's mouth is a complicated, multi-step process. In order to anchor the restoration in the patient's mouth, a dental implant is placed into the patient's jaw or skull. This implant provides an anchoring device for the abutment and screw which will eventually secure the restoration, e.g., a replacement tooth or bridge. However, it often is difficult to locate sufficient maxillary (sinus) or mandibular (jaw) bone within which to fix the implant, so that an adequate foundation and proper positioning of the restoration may be achieved. Because the underlying bone structure and its density or mass may not be readily apparent on radiographs, implants may inadvertently be positioned in bone structure of insufficient density or mass to form a proper foundation for the implant. This may ultimately lead to the implant's failure. In addition, an implant seated at an improper angle may have an unaesthetic appearance, and an improperly seated implant may result in a malocclusion. Preoperative radiographic evaluations, such as conventional radiographs, X-ray images, CAT-scans, and the like, are used in combination with dental (or medical) stents to determine the proper site and angle of implantation.
The orientation of dental implants is usually governed by the existing anatomy and the desired position of the restoration(s). Once a functionally and esthetically desirable implant location has been identified, stents are fabricated to allow preferred positioning of the implant in the underlying bone. At the time of surgery, the anatomic information obtained from the radiographic evaluation is correlated with the desired implant location, as indicated by the stent, to position the implant at the preferred location and orientation. However, it is desirable to correlate the information obtained from the radiographic evaluation and the stent prior to surgery.
The stent is placed in a patient's mouth and is aligned with the location at which an implant is to be placed. A radiographic image is taken of the patient's mouth showing the position of the stent. By examining the radiographic image, a dentist, oral surgeon, or periodontist may determine whether sufficient bone exists under the stent to support the implant. If insufficient bone is present, additional bone may be grafted to the patient's sinus or jaw, a different location for the periodontal implant may be chosen, or a different mode of treatment eliminating the use of an implant may be selected. If sufficient bone is present, however, the stent may later be used to guide the placement of the implant. The stent may either be transparent or translucent and may have guide holes or slots through which the implant may be positioned. Thus, stents preferably possess two qualities: (1) they are radiographically opaque and (2) they are visually translucent or transparent.
Stents may be fabricated by technicians from an acrylic resin. However, acrylic resin is radio-lucent, i.e., not radio-opaque. The stent may be made radio-opaque by the addition of a radio-opaque powder, such as barium sulfate powder, to the acrylic resin during the fabrication of the stent. Many procedures or recipes for preparing stents containing barium sulfate are possible and are used. Generally, however, technicians simply mix a quantity of radio-opaque powder into the acrylic resin base. Such powders are readily available from medical and dental laboratory supply companies. Although, barium sulfate is a frequently used radio-opaque powder, other radio-opaque powders, such as metal powders, also are used. Nevertheless, metal powders or metal flakes tend to reflect or deflect the X-rays, which may cause unsatisfactory radiographs and uncontrolled or blurred exposure.
The lack of a standardized procedure or recipe, however, is a disadvantage of the current methods of fabricating radio-opaque stents. Unless the barium sulfate powder is added in the proper quantity and is thoroughly mixed in the acrylic material, the opacity of the stent may be uneven. Further, settling may occur during the hardening of the acrylic, which may create additional unevenness in the opacity. If the stent is not uniformly radio-opaque, it may be difficult to properly locate the position for the proposed implant. Therefore, existing radio-opaque medical stents may not provide an accurate determination of proper drilling angles for positioning of implants and may create distortion in the radiographs, for example, due to the presence of metallic powders or flakes.